Magnetic recording medium

Abstract

A magnetic recording medium, comprising a magnetic layer containing a ferromagnetic metal thin film having micro-size projections on surface thereof and formed by vacuum film forming method and provided at least on one side of a nonmagnetic substrate, a carbon protective layer and a lubricant provided on said magnetic layer, a central axis of a diamond indenter of trilateral pyramid having a tip sharp angle of 90° and a radius of curvature at tip of 35-50 nm being directed perpendicularly to the surface of the nonmagnetic substrate, pressure is applied on the carbon protective layer, and a load obtained when indentation depth of the indenter is 10-25 nm is divided by projection area of indenter contactor, and the quotient, i.e. micro-hardness, is within the range of 10-30 GPa.

What is claimed is:  
     
       1. A magnetic recording medium, comprising a magnetic layer containing a ferromagnetic metal thin film having micro-size projections on surface thereof and formed by vacuum film forming method and provided at least on one side of a nonmagnetic substrate, a carbon protective layer and a lubricant provided on said magnetic layer, a central axis of a diamond indenter of trilateral pyramid having a tip sharp angle of 90° and a radius of curvature at tip of 35-50 nm being directed perpendicularly to the surface of the nonmagnetic substrate, pressure is applied on the carbon protective layer, and a load obtained when indentation depth of the indenter is 10-25 nm is divided by projection area of indenter contactor, and the quotient, i.e. micro-hardness, is within the range of 10-30 GPa. 
     
     
       2. A magnetic recording medium according to  claim 1 , wherein said nonmagnetic substrate is a flexible plastic substrate, and the magnetic recording medium is a disk-type magnetic recording medium. 
     
     
       3. A magnetic recording medium according to  claim 1 , wherein thickness of the carbon protective film is within the range of 2.5 to 30 nm. 
     
     
       4. A magnetic recording medium according to  claim 2 , wherein thickness of the carbon protective film is within the range of 2.5 to 30 nm. 
     
     
       5. A magnetic recording medium according to  claim 1 , wherein the carbon protective layer is formed using ethylene as raw material gas. 
     
     
       6. A magnetic recording medium according to  claim 2 , wherein the carbon protective layer is formed using ethylene as raw material gas. 
     
     
       7. A magnetic recording medium according to  claim 3 , wherein the carbon protective layer is formed using ethylene as raw material gas. 
     
     
       8. A magnetic recording medium according to  claim 4 , wherein the carbon protective layer is formed using ethylene as raw material gas. 
     
     
       9. A magnetic recording medium according to  claim 1 , wherein the nonmagnetic substrate is aramide film or polyimide film. 
     
     
       10. A magnetic recording medium according to  claim 2 , wherein the nonmagnetic substrate is aramide film or polyimide film. 
     
     
       11. A magnetic recording medium according to  claim 3 , wherein the nonmagnetic substrate is aramide film or polyimide film. 
     
     
       12. A magnetic recording medium according to  claim 4 , wherein the nonmagnetic substrate is aramide film or polyimide film. 
     
     
       13. A magnetic recording medium according to  claim 5 , wherein the nonmagnetic substrate is aramide film or polyimide film. 
     
     
       14. A magnetic recording medium according to  claim 6 , wherein the nonmagnetic substrate is aramide film or polyimide film. 
     
     
       15. A magnetic recording medium according to  claim 7 , wherein the nonmagnetic substrate is aramide film or polyimide film. 
     
     
       16. A magnetic recording medium according to  claim 8 , wherein the nonmagnetic substrate is aramide film or polyimide film. 
     
     
       17. A magnetic recording medium according to one of  claims 1  to  16 , wherein an undercoating film comprising polyimide resin or organopolysiloxane is formed on the nonmagnetic substrate.